Magnetoresistive effect device

ABSTRACT

A magnetoresistive effect device includes a magnetoresistive effect element including a magnetization fixed layer, a spacer layer, and a magnetization free layer; a first port; a second port; a signal line; an impedance element; and a direct-current input terminal. The first port, the magnetoresistive effect element, and the second port are connected in series in this order via the signal line. The impedance element is connected to ground and to the signal line between the magnetoresistive effect element and the first port or the second port. The direct-current input terminal is connected to the signal line at the opposite side to the impedance element with the magnetoresistive effect element in between the direct-current input terminal and the impedance element. A closed circuit including the magnetoresistive effect element, the signal line, the impedance element, the ground, and the direct-current input terminal is to be formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetoresistive effect deviceincluding a magnetoresistive effect element.

2. Description of the Related Art

The speed of wireless communication has increased in recent years withthe increasing functions of mobile communication terminals, such asmobile phones. Since the communication speed is proportional to the bandwidth of frequencies that are used, the number of frequency bandsnecessary for communication is increased. Accordingly, the number ofhigh-frequency filters that are mounted in mobile communicationterminals is increased. Spintronics has been studied in recent years asa field that is probably applicable to new high-frequency components.One phenomenon that has received attention is the spin torque resonancephenomenon, which is caused by a magnetoresistive effect element (referto Nature, Vol. 438, No. 7066, pp. 339 to 342 17 Nov. 2005). Applicationof an alternating current to a magnetoresistive effect element causesspin torque resonance in the magnetoresistive effect element, and theresistance value of the magnetoresistive effect element oscillates witha fixed cycle at a frequency corresponding to a spin torque resonancefrequency. The spin torque resonance frequency of the magnetoresistiveeffect element varies with the strength of the magnetic field applied tothe magnetoresistive effect element. The spin torque resonance frequencyof the magnetoresistive effect element is generally within ahigh-frequency band from several gigahertz to several tens of gigahertz.

SUMMARY OF THE INVENTION

Although the magnetoresistive effect element may be applied to ahigh-frequency device, utilizing the spin torque resonance phenomenon,specific configurations to apply the magnetoresistive effect element tothe high-frequency device, such as the high-frequency filter, have notbeen proposed. Accordingly, the present invention aims to provide amagnetoresistive effect device capable of realizing a high-frequencydevice, such as a high-frequency filter, that includes amagnetoresistive effect element.

A magnetoresistive effect device according to an embodiment of thepresent invention includes at least one magnetoresistive effect elementincluding a magnetization fixed layer, a spacer layer, and amagnetization free layer, the direction of magnetization of which iscapable of being varied; a first port through which a high-frequencysignal is input; a second port through which a high-frequency signal isoutput; a signal line; an impedance element; and a direct-current inputterminal. The first port, the magnetoresistive effect element, and thesecond port are connected in series in this order via the signal line.The impedance element is connected to ground and to the signal linebetween the magnetoresistive effect element and the first port or thesecond port. The direct-current input terminal is connected to thesignal line at the opposite side to the impedance element with themagnetoresistive effect element in between the direct-current inputterminal and the impedance element. A closed circuit including themagnetoresistive effect element, the signal line, the impedance element,the ground, and the direct-current input terminal is to be formed.

In the present invention, an “impedance element” is used to mean a chokecoil or a resistance element. In addition, in the present invention, the“choke coil” is used as a generic term of elements having a function tocut off high-frequency components of current with inductor componentsand pass direct current components of the current.

With the above magnetoresistive effect device, the input of thehigh-frequency signal from the first port to the magnetoresistive effectelement via the signal line enables the spin torque resonance to beinduced in the magnetoresistive effect element. Due to the spin torqueresonance, the magnetoresistive effect element may be considered as anelement in which the resistance value oscillates with a fixed cycle at afrequency corresponding to the spin torque resonance frequency. Withthis effect, the element impedance at the frequency equal to the spintorque resonance frequency of the magnetoresistive effect element isreduced. The connection of the first port, the magnetoresistive effectelement, and the second port through which the high-frequency signal isoutput in series in this order enables the high-frequency signal to becut off at a non-resonant frequency with high impedance and to be passedat a resonant frequency with low impedance. In other words, themagnetoresistive effect device is capable of having frequencycharacteristics as a high-frequency filter.

The impedance element connected to the signal line and the ground doesnot pass the high-frequency signal but selectively causes the directcurrent signal to flow to the ground. Accordingly, the direct currentsupplied from the direct-current input terminal flows through the closedcircuit including the magnetoresistive effect element, the signal line,the impedance element, the ground, and the direct-current inputterminal. The closed circuit allows the direct current to be efficientlyapplied to the magnetoresistive effect element. In response to theapplication of the direct current, the spin torque is increased and theamplitude of the oscillating resistance value is increased in themagnetoresistive effect element. Since the increase in the amplitude ofthe oscillating resistance value increases the amount of change inelement impedance of the magnetoresistive effect element, themagnetoresistive effect device functions as a high-frequency filterhaving a wide range of cut-off characteristics and bandpasscharacteristics.

In addition, since varying the direct current applied from thedirect-current input terminal enables the spin torque resonancefrequency of the magnetoresistive effect element to be variablycontrolled, the magnetoresistive effect device functions as a variablefrequency filter.

The magnetoresistive effect device may further include at least onemagnetic-field applying mechanism for applying a magnetic field to themagnetoresistive effect element.

In the magnetoresistive effect device, the magnetic-field applyingmechanism may vary the magnetic field to vary a spin torque resonancefrequency of the magnetoresistive effect element.

With the above magnetoresistive effect device, since the spin torqueresonance frequency of the magnetoresistive effect element is capable ofbeing variably controlled, the magnetoresistive effect device functionsas the variable frequency filter.

In the magnetoresistive effect device, the at least one magnetoresistiveeffect element may include a plurality of magnetoresistive effectelements having different spin torque resonance frequencies from eachother, and the magnetoresistive effect elements may be connected inparallel to each other.

With the above magnetoresistive effect device, since themagnetoresistive effect elements having different spin torque resonancefrequencies from each other are connected in parallel to each other, theimpedance of the multiple magnetoresistive effect elements near themultiple frequencies equal to the spin torque resonance frequencies ofthe respective magnetoresistive effect elements is reduced, and apassband having a certain width is provided. In addition, varying thedirect current or the magnetic field to be applied to themagnetoresistive effect elements enables the positions of the passbandsto be varied. Accordingly, the magnetoresistive effect device functionsas a variable frequency filter capable of varying the position of thepassband.

In addition, the combined impedance of the multiple magnetoresistiveeffect elements near the spin torque resonance frequencies of themultiple magnetoresistive effect elements connected in parallel to eachother is lower than the impedance of each of the magnetoresistive effectelements, and the passband loss of the filter is reduced. Accordingly,the magnetoresistive effect device functions as a high-frequency filterhaving excellent characteristics.

In the magnetoresistive effect device, the at least one magnetoresistiveeffect element may include a plurality of magnetoresistive effectelements, the at least one magnetic-field applying mechanism may includea plurality of magnetic-field applying mechanisms, and themagnetoresistive effect elements may be connected in parallel to eachother and the magnetic-field applying mechanisms are provided so as toapply an individual magnetic field to each of the magnetoresistiveeffect elements.

With the above magnetoresistive effect device, since themagnetoresistive effect device has the multiple magnetic-field applyingmechanisms so as to apply an individual magnetic field to each of themultiple magnetoresistive effect elements, the magnetoresistive effectdevice is capable of individually controlling the spin torque resonancefrequencies of the respective magnetoresistive effect elements. Inaddition, since the multiple magnetoresistive effect elements areconnected in parallel to each other, the impedance of the multiplemagnetoresistive effect elements near the multiple frequencies equal tothe spin torque resonance frequencies of the respective magnetoresistiveeffect elements is reduced, and a passband having a certain width isprovided. Furthermore, varying the direct current or the magnetic fieldto be applied to each of the magnetoresistive effect elements enablesthe bandwidth of the magnetoresistive effect device to be arbitrarilyvaried. Accordingly, the magnetoresistive effect device functions as avariable frequency filter capable of arbitrarily varying the passband.

In the magnetoresistive effect device, the at least one magnetoresistiveeffect element may include a plurality of magnetoresistive effectelements having different spin torque resonance frequencies from eachother, and the magnetoresistive effect elements may be connected inseries to each other.

With the above magnetoresistive effect device, since the multiplemagnetoresistive effect elements having different spin torque resonancefrequencies from each other are connected in series to each other, theimpedance of the multiple magnetoresistive effect elements near themultiple frequencies equal to the spin torque resonance frequencies ofthe respective magnetoresistive effect elements is reduced, and apassband having a certain width is provided. In addition, varying thedirect current or the magnetic field to be applied to themagnetoresistive effect elements enables the positions of the passbandsto be varied. Accordingly, the magnetoresistive effect device functionsas the variable frequency filter capable of varying the position of thepassband.

In the magnetoresistive effect device, the at least one magnetoresistiveeffect element may include a plurality of magnetoresistive effectelements, the at least one magnetic-field applying mechanism may includea plurality of magnetic-field applying mechanisms, and themagnetoresistive effect elements may be connected in series to eachother and the magnetic-field applying mechanisms are provided so as toapply an individual magnetic field to each of the magnetoresistiveeffect elements.

With the above magnetoresistive effect device, since themagnetoresistive effect device has the multiple magnetic-field applyingmechanisms so as to apply an individual magnetic field to each of themultiple magnetoresistive effect elements, the magnetoresistive effectdevice is capable of individually controlling the spin torque resonancefrequencies of the respective magnetoresistive effect elements. Inaddition, since the multiple magnetoresistive effect elements areconnected in series to each other, the impedance of the multiplemagnetoresistive effect elements near the multiple frequencies equal tothe spin torque resonance frequencies of the respective magnetoresistiveeffect elements is reduced, and a passband having a certain width isprovided. Furthermore, varying the direct current or the magnetic fieldto be applied to each of the magnetoresistive effect elements enablesthe bandwidth of the magnetoresistive effect device to be arbitrarilyvaried. Accordingly, the magnetoresistive effect device functions as thevariable frequency filter capable of arbitrarily varying the passband.

In the magnetoresistive effect device, plan view shapes of themagnetoresistive effect elements having different spin torque resonancefrequencies from each other may have different aspect ratios from eachother. Here, “plan view shapes” mean the shapes of the magnetoresistiveeffect elements when the magnetoresistive effect elements are viewedfrom above a plane perpendicular to the stacking direction of therespective layers composing the magnetoresistive effect elements. “Theaspect ratio” means the ratio of the length of long sides to the lengthof short sides of a rectangle circumscribed around the plan view shapeof the magnetoresistive effect element with a minimum area.

With the above magnetoresistive effect device, since the plan viewshapes of the multiple magnetoresistive effect elements having differentspin torque resonance frequencies from each other have different aspectratios from each other, it is possible to manufacture the multiplemagnetoresistive effect elements having different spin torque resonancefrequencies from each other through the same process. Specifically,since the multiple magnetoresistive effect elements have the same filmstructure in the magnetoresistive effect device, it is possible tocollectively form the films of the layers composing the multiplemagnetoresistive effect elements.

In the magnetoresistive effect device, the magnetoresistive effectdevice may not include a magnetoresistive effect element connected tothe signal line and the ground in parallel with the second port.

With the above magnetoresistive effect device, since a magnetoresistiveeffect element connected to the signal line and the ground in parallelwith the second port is not included, the magnetoresistive effect deviceis capable of preventing the input high-frequency signal from flowinginto the ground to prevent an increase in loss of the high-frequencysignal. The flow of the high-frequency signal into the ground is causedby a reduction in impedance at the spin torque resonance frequency ofthe magnetoresistive effect element connected to the signal line and theground in parallel with the second port. Accordingly, themagnetoresistive effect device functions as a high-frequency filterhaving excellent bandpass characteristics.

According to the present invention, the magnetoresistive effect devicecapable of realizing a high-frequency device, such as a high-frequencyfilter, including the magnetoresistive effect element is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a magnetoresistive effectdevice according to a first embodiment.

FIG. 2 is a graph illustrating the relationship between frequency andattenuation for direct current in the magnetoresistive effect deviceaccording to the first embodiment.

FIG. 3 is a graph illustrating the relationship between the frequencyand the attenuation for the strength of a magnetic field in themagnetoresistive effect device according to the first embodiment.

FIG. 4 is a schematic cross-sectional view of a magnetoresistive effectdevice according to a second embodiment.

FIG. 5 is a top view of the magnetoresistive effect device according tothe second embodiment.

FIG. 6 is a graph illustrating the relationship between the frequencyand the attenuation in the magnetoresistive effect device according tothe second embodiment.

FIG. 7 is a schematic cross-sectional view of a magnetoresistive effectdevice according to a third embodiment.

FIG. 8 is a graph illustrating the relationship between the frequencyand the attenuation in the magnetoresistive effect device according tothe third embodiment.

FIG. 9 is a schematic cross-sectional view of a magnetoresistive effectdevice according to a fourth embodiment.

FIG. 10 is a top view of the magnetoresistive effect device according tothe fourth embodiment.

FIG. 11 is a graph illustrating the relationship between the frequencyand the attenuation in the magnetoresistive effect device according tothe fourth embodiment.

FIG. 12 is a schematic cross-sectional view of a magnetoresistive effectdevice according to a fifth embodiment.

FIG. 13 is a graph illustrating the relationship between the frequencyand the attenuation in the magnetoresistive effect device according tothe fifth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will herein be described in detailwith reference to the attached drawings. The present invention is notlimited by the content described in the following embodiments.Components described below include components easily supposed by personsskilled in the art, components substantially equivalent to each other,and components within an equivalent range. In addition, the componentsdescribed below may be appropriately combined with each other.Furthermore, the components may be omitted, replaced, or modifiedwithout departing from the true spirit and scope of the invention.

First Embodiment

FIG. 1 is a schematic cross-sectional view of a magnetoresistive effectdevice 100 according to a first embodiment of the present invention. Themagnetoresistive effect device 100 includes a magnetoresistive effectelement 1 a including a magnetization fixed layer 2, a spacer layer 3,and a magnetization free layer 4, an upper electrode 5, a lowerelectrode 6, a first port 9 a, a second port 9 b, a signal line 7, achoke coil 10 as an impedance element, a direct-current input terminal11, and a magnetic-field applying mechanism 12. The first port 9 a, themagnetoresistive effect element 1 a, and the second port 9 b areconnected in series in this order via the signal line 7. The choke coil10 is connected to ground 8 and to the signal line 7 between themagnetoresistive effect element 1 a and the second port 9 b. Thedirect-current input terminal 11 is connected to the signal line 7 atthe opposite side to the choke coil 10 with the magnetoresistive effectelement 1 a in between the direct-current input terminal 11 and thechoke coil 10. Connection of a direct-current source 13 connected to theground 8 to the direct-current input terminal 11 forms a closed circuitincluding the magnetoresistive effect element 1 a, the signal line 7,the choke coil 10, the ground 8, and the direct-current input terminal11. The magnetoresistive effect device 100 does not include amagnetoresistive effect element connected to the signal line 7 and theground 8 in parallel with the second port 9 b.

The first port 9 a is an input port through which a high-frequencysignal, which is an alternating current signal, is input and the secondport 9 b is an output port through which a high-frequency signal isoutput. The signal line 7 is electrically connected to themagnetoresistive effect element 1 a via the upper electrode 5 and thelower electrode 6 so as to sandwich the magnetoresistive effect element1 a. The high-frequency signal input through the first port 9 a flowsthrough the magnetoresistive effect element 1 a and is supplied to thesecond port 9 b. Attenuation (S21), which is a dB value of a power ratio(output power/input power) when the high-frequency signal is suppliedfrom the first port 9 a to the second port 9 b, may be measured by ahigh-frequency measuring device, such as a network analyzer.

The upper electrode 5 and the lower electrode 6 serve as a pair ofelectrodes and are disposed in the stacking direction of the respectivelayers composing the magnetoresistive effect element 1 a with themagnetoresistive effect element 1 a sandwiched therebetween.Specifically, the upper electrode 5 and the lower electrode 6 functionas a pair of electrodes to cause a signal (current) to flow through themagnetoresistive effect element 1 a in a direction intersecting with theface of each layer composing the magnetoresistive effect element 1 a,for example, in a direction (stacking direction) perpendicular to theface of each layer composing the magnetoresistive effect element 1 a.Each of the upper electrode 5 and the lower electrode 6 is preferablycomposed of a film made of Ta, Cu, Au, AuCu, or Ru or a film made of twoor more of the above materials. One end (at the magnetization free layer4 side) of the magnetoresistive effect element 1 a is electricallyconnected to the signal line 7 via the upper electrode 5 and the otherend (at the magnetization fixed layer 2 side) of the magnetoresistiveeffect element 1 a is electrically connected to the signal line 7 viathe lower electrode 6.

The ground 8 functions as reference voltage. The shape of the signalline 7 with the ground 8 is preferably of a micro strip line (MSL) typeor a coplanar waveguide (CPW) type. In design of the micro strip lineshape or the coplanar waveguide shape, designing the width of the signalline 7 and the distance to the ground so that the characteristicimpedance of the signal line 7 is equal to the impedance of a circuitsystem enables the transmission loss through the signal line 7 to bereduced.

The choke coil 10 is connected between the signal line 7 and the ground8 and has a function to cut off high-frequency components of currentwith its inductance component and pass direct-current components of thecurrent. In the present specification, the “choke coil” is used as ageneric term of elements having a function to cut off high-frequencycomponents of current with inductor components and pass direct currentcomponents of the current. The choke coil 10 may be a chip inductor oran inductor composed of a pattern line. Alternatively, the choke coil 10may be a resistance element having an inductance component. The chokecoil 10 preferably has an inductance value of 10 nH or more. The use ofthe choke coil 10 enables direct current applied from the direct-currentinput terminal 11 to flow through the closed circuit including themagnetoresistive effect element 1 a, the signal line 7, the choke coil10, the ground 8, and the direct-current input terminal 11 withoutdegrading the characteristics of the high-frequency signal passingthrough the magnetoresistive effect element 1 a.

The direct-current input terminal 11 is connected to the signal line 7at the opposite side to the choke coil 10 with the magnetoresistiveeffect element 1 a in between the direct-current input terminal 11 andthe choke coil 10. More specifically, the direct-current input terminal11 is connected to the signal line 7 between the magnetoresistive effectelement 1 a and the first port 9 a. The connection of the direct-currentsource 13 to the direct-current input terminal 11 enables the directcurrent to be applied to the magnetoresistive effect element 1 a. In themagnetoresistive effect device 100 illustrated in FIG. 1, the directcurrent flowing from the magnetization free layer 4 to the magnetizationfixed layer 2 in the magnetoresistive effect element 1 a is applied tothe magnetoresistive effect element 1 a. A choke coil or a resistanceelement for cutting off the high-frequency signal may be connected inseries between the direct-current input terminal 11 and thedirect-current source 13.

The direct-current source 13 is connected to the ground 8 and thedirect-current input terminal 11 and applies the direct current from thedirect-current input terminal 11 to the closed circuit including themagnetoresistive effect element 1 a, the signal line 7, the choke coil10, the ground 8, and the direct-current input terminal 11. Thedirect-current source 13 is composed of, for example, a circuit in whicha variable resistor is combined with a direct-current voltage source andis capable of varying the current value of the direct current. Thedirect-current source 13 may be composed of a circuit which is capableof generating constant direct current and in which a fixed resistor iscombined with a direct-current voltage source.

The magnetic-field applying mechanism 12 is disposed near themagnetoresistive effect element 1 a and applies a magnetic field to themagnetoresistive effect element 1 a. For example, the magnetic-fieldapplying mechanism 12 is of an electromagnetic type or a strip line typecapable of variably controlling the strength of the applied magneticfield using voltage or current. Alternatively, the magnetic-fieldapplying mechanism 12 may be a combination of the electromagnetic typeor the strip line type with a permanent magnet that supplies only aconstant magnetic field. In addition, the magnetic-field applyingmechanism 12 varies the magnetic field to be applied to themagnetoresistive effect element 1 a to enable the spin torque resonancefrequency of the magnetoresistive effect element 1 a to be varied.

The magnetization fixed layer 2 is made of a ferromagnetic material andthe magnetization direction of the magnetization fixed layer 2 issubstantially fixed to one direction. The magnetization fixed layer 2 ispreferably made of a material having high spin polarizability, such asFe, Co, Ni, an alloy of Ni and Fe, an alloy of Fe and Co, or an ally ofFe, Co, and B. This achieves a high magnetoresistive change rate. Themagnetization fixed layer 2 may be made of a Heusler alloy. Themagnetization fixed layer 2 preferably has a film thickness of 1 nm to10 nm. An antiferromagnetic layer may be added so as to be in contactwith the magnetization fixed layer 2 in order to fix the magnetizationof the magnetization fixed layer 2. Alternatively, the magnetization ofthe magnetization fixed layer 2 may be fixed using magnetic anisotropycaused by the crystal structure of the magnetization fixed layer 2 orthe shape thereof. The antiferromagnetic layer may be made of FeO, CoO,NiO, CuFeS₂, IrMn, FeMn, PtMn, Cr, or Mn.

The spacer layer 3 is arranged between the magnetization fixed layer 2and the magnetization free layer 4. The magnetization of themagnetization fixed layer 2 and the magnetization of the magnetizationfree layer 4 interact with each other to achieve the magnetoresistiveeffect. The spacer layer 3 may be formed of a layer made of a conductivematerial, an insulating material, or a semiconductor material.Alternatively, the spacer layer 3 may be formed of a layer in which acurrent flow point composed of a conductor is included in an insulator.

When a non-magnetic conductive material is used for the spacer layer 3,the non-magnetic conductive material may be Cu, Ag, Au, or Ru. In thiscase, a giant magnetoresistive (GMR) effect is produced in themagnetoresistive effect element 1 a. When the GMR effect is used, thespacer layer 3 preferably has a film thickness of about 0.5 nm to 3.0nm.

When a non-magnetic insulating material is used for the spacer layer 3,the non-magnetic insulating material may be Al₂O₃ or MgO. In this case,a tunnel magnetoresistive (TMR) effect is produced in themagnetoresistive effect element 1 a. Adjusting the film thickness of thespacer layer 3 so that a coherent tunnel effect is produced between themagnetization fixed layer 2 and the magnetization free layer 4 achievesa high magnetoresistive change rate. When the TMR effect is used, thespacer layer 3 preferably has a film thickness of about 0.5 nm to 3.0nm.

When a non-magnetic semiconductor material is used for the spacer layer3, the non-magnetic semiconductor material may be ZnO, In₂O₃, SnO₂, ITO,GaO_(x), or Ga₂O_(x). The spacer layer 3 preferably has a film thicknessof about 1.0 nm to 4.0 nm.

When a layer in which the current flow point composed of a conductor isincluded in a non-magnetic insulator is used as the spacer layer 3, thespacer layer 3 preferably has a structure in which the current flowpoint composed of a conductor made of, for example, CoFe, CoFeB, CoFeSi,CoMnGe, CoMnSi, CoMnAl, Fe, Co, Au, Cu, Al, or Mg is included in themon-magnetic insulator made of Al₂O₃ or MgO. In this case, the spacerlayer 3 preferably has a film thickness of about 0.5 nm to 2.0 nm.

The direction of the magnetization of the magnetization free layer 4 iscapable of being varied with an externally applied magnetic field orspin polarized electrons. The magnetization free layer 4 is made of aferromagnetic material. When the magnetization free layer 4 is made of amaterial having a magnetic easy axis in an in-plane direction, thematerial may be, for example, CoFe, CoFeB, CoFeSi, CoMnGe, CoMnSi, orCoMnAl. The magnetization free layer 4 preferably has a film thicknessof about 1 nm to 10 nm. When the magnetization free layer 4 is made of amaterial having the magnetic easy axis in a plane normal direction, thematerial may be, for example, Co, a CoCr-based alloy, a Co multilayerfilm, a CoCrPt-based alloy, an FePt-based alloy, an SmCo-based alloyincluding rare earth, or a TbFeCo alloy. The magnetization free layer 4may be made of a Heusler alloy. A material having high spinpolarizability may be disposed between the magnetization free layer 4and the spacer layer 3. This achieves the high magnetoresistive changerate. The material having high spin polarizability may be, for example,a CoFe alloy or a CoFeB alloy. Each of the CoFe alloy and the CoFeBalloy preferably has a film thickness of about 0.2 nm to 1.0 nm.

A cap layer, a seed layer, or a buffer layer may be provided between theupper electrode 5 and the magnetoresistive effect element 1 a andbetween the lower electrode 6 and the magnetoresistive effect element 1a. Each of the cap layer, the seed layer, and the buffer layer may bemade of Ru, Ta, Cu, or Cr or may be formed of a stacked film including aRu layer, a Ta layer, a Cu layer, and a Cr layer. The cap layer, theseed layer, and the buffer layer preferably each have a film thicknessof about 2 nm to 10 nm.

When the magnetoresistive effect element 1 a has a rectangular shape(including a square shape) in plan view, the magnetoresistive effectelement 1 a desirably has long sides of about 100 nm or 100 nm or less.When the magnetoresistive effect element 1 a does not have a rectangularshape in plan view, the long sides of a rectangle circumscribed aroundthe plan view shape of the magnetoresistive effect element 1 a with aminimum area are defined as the long sides of the magnetoresistiveeffect element 1 a. When the long sides of the magnetoresistive effectelement 1 a are short, for example, about 100 nm, the magnetization ofthe magnetization free layer 4 is capable of having a single magneticdomain to realize the spin torque resonance phenomenon with highefficiency. The “plan view shape” means the shape of themagnetoresistive effect element when the magnetoresistive effect elementis viewed from above a plane perpendicular to the stacking direction ofthe respective layers composing the magnetoresistive effect element.

The spin torque resonance phenomenon will now be described.

Upon input of the high-frequency signal of a frequency equal to the spintorque resonance frequency specific to the magnetoresistive effectelement 1 a, the magnetization of the magnetization free layer 4oscillates at the spin torque resonance frequency. This phenomenon iscalled the spin torque resonance phenomenon. The element resistancevalue of the magnetoresistive effect element 1 a is determined by therelative angle between the magnetization of the magnetization fixedlayer 2 and the magnetization of the magnetization free layer 4.Accordingly, the resistance value of the magnetoresistive effect element1 a in the spin torque resonance varies with a fixed cycle with theoscillation of the magnetization of the magnetization free layer 4. Inother words, the magnetoresistive effect element 1 a is capable of beingconsidered as a resistor oscillation element in which the resistancevalue varies with a fixed cycle at the spin torque resonance frequency.In addition, upon input of the high-frequency signal of a frequencyequal to the spin torque resonance frequency into the resistoroscillation element, the phase of the magnetic field is synchronizedwith the phase of the high-frequency signal and the impedance for thehigh-frequency signal is reduced. In other words, the magnetoresistiveeffect element 1 a is capable of being considered as a resistanceelement in which the impedance of the high-frequency signal is reducedat the spin torque resonance frequency due to the spin torque resonancephenomenon. The spin torque resonance frequency is increased with anincrease in strength of the magnetic field applied to themagnetoresistive effect element 1 a.

The application of the direct current to the magnetoresistive effectelement 1 a in the spin torque resonance increases the spin torque toincrease the amplitude of the oscillating resistance value. The increasein the amplitude of the oscillating resistance value increases theamount of change in element impedance of the magnetoresistive effectelement 1 a. The spin torque resonance frequency is reduced with anincrease in current density of the applied direct current. Accordingly,the spin torque resonance frequency of the magnetoresistive effectelement 1 a is capable of being varied by varying the magnetic fieldfrom the magnetic-field applying mechanism 12 or by varying the directcurrent applied from the direct-current input terminal 11.

Due to the spin torque resonance phenomenon, the frequency componentsthat coincide with the spin torque resonance frequency of themagnetoresistive effect element 1 a or that are near the spin torqueresonance frequency of the magnetoresistive effect element 1 a, amongthe high-frequency components of the high-frequency signal input throughthe first port 9 a, pass through the magnetoresistive effect element 1 ain a low impedance state and are supplied to the second port 9 b. Inother words, the magnetoresistive effect device 100 functions as ahigh-frequency filter using the frequencies near the spin torqueresonance frequency of the magnetoresistive effect element 1 a as apassband.

FIG. 2 and FIG. 3 are graphs each illustrating the relationship betweenthe frequency of the high-frequency signal input into themagnetoresistive effect device 100 and the attenuation. Referring toFIG. 2 and FIG. 3, the vertical axis represents attenuation and thehorizontal axis represents frequency. FIG. 2 is a graph when a constantmagnetic field is applied to the magnetoresistive effect element 1 a.Referring to FIG. 2, a plot line 100 a 1 represents the relationshipbetween the high-frequency signal and the attenuation when the directcurrent applied from the direct-current input terminal 11 to themagnetoresistive effect element 1 a has a value of Ia1 and a plot line100 a 2 represents the relationship between the high-frequency signaland the attenuation when the direct current applied from thedirect-current input terminal 11 to the magnetoresistive effect element1 a has a value of Ia2. The relationship between the applied directcurrent values is Ia1<Ia2. FIG. 3 is a graph when constant directcurrent is applied to the magnetoresistive effect element 1 a. Referringto FIG. 3, a plot line 100 b 1 represents the relationship between thehigh-frequency signal and the attenuation when the magnetic fieldapplied from the magnetic-field applying mechanism 12 to themagnetoresistive effect element 1 a has a strength of Hb1 and a plotline 100 b 2 represents the relationship between the high-frequencysignal and the attenuation when the magnetic field applied from themagnetic-field applying mechanism 12 to the magnetoresistive effectelement 1 a has a strength of Hb2. The relationship between thestrengths of the magnetic fields is Hb1<Hb2.

For example, when the value of the direct current applied from thedirect-current input terminal 11 to the magnetoresistive effect element1 a is increased from Ia1 to Ia2, as illustrated in FIG. 2, the amountof reduction in element impedance at the frequencies near the spintorque resonance frequency of the magnetoresistive effect element 1 a(the frequencies in the passband) is increased with the variation in thecurrent value. As a result, the high-frequency signal output from thesecond port 9 b is further increased to reduce the attenuation (theabsolute value of the attenuation). Accordingly, the magnetoresistiveeffect device 100 is capable of realizing a high-frequency filter havinga wide range of cut-off characteristics and bandpass characteristics. Inresponse to the increase of the direct current value from Ia1 to Ia2 thespin torque resonance frequency of the magnetoresistive effect element 1a is shifted from fa1 to fa2. In other words, the passband is shiftedtoward low frequencies. Thus, the magnetoresistive effect device 100 mayfunction as a high-frequency filter capable of varying the frequenciesof the passband.

Furthermore, when the strength of the magnetic field applied from themagnetic-field applying mechanism 12 is increased from Hb1 to Hb2, asillustrated in FIG. 3, the spin torque resonance frequency of themagnetoresistive effect element 1 a is shifted from fb1 to fb2. In otherwords, the passband is shifted toward high frequencies. The passband iscapable of being greatly shifted when the strength of the magnetic fieldis varied, compared with a case in which the direct current value isvaried. In other words, the magnetoresistive effect device 100 mayfunction as the high-frequency filter capable of varying the frequenciesof the passband.

When the passband is varied, the phase of a passing signal is variedwhen attention is focused on a certain frequency in the passband. Inother words, the magnetoresistive effect device 100 may also function asa phase shifter capable of varying the phase of a signal of a frequencyin the passband.

As described above, the magnetoresistive effect device 100 includes themagnetoresistive effect element 1 a including the magnetization fixedlayer 2, the spacer layer 3, and the magnetization free layer 4 thedirection of magnetization of which is capable of being varied; thefirst port 9 a; the second port 9 b; the signal line 7; the choke coil10 (impedance element); and the direct-current input terminal 11. Thefirst port 9 a, the magnetoresistive effect element 1 a, and the secondport 9 b are connected in series in this order via the signal line 7.The choke coil 10 (impedance element) is connected to the ground 8 andto the signal line 7 between the magnetoresistive effect element 1 a andthe second port 9 b. The direct-current input terminal 11 is connectedto the signal line 7 at the opposite side to the choke coil 10(impedance element) with the magnetoresistive effect element 1 a inbetween the direct-current input terminal 11 and the choke coil 10(impedance element). The closed circuit including the magnetoresistiveeffect element 1 a, the signal line 7, the choke coil 10 (impedanceelement), the ground 8, and the direct-current input terminal 11 is tobe formed.

Accordingly, the input of the high-frequency signal from the first port9 a to the magnetoresistive effect element 1 a via the signal line 7enables the spin torque resonance to be induced in the magnetoresistiveeffect element 1 a. Due to the spin torque resonance, themagnetoresistive effect element 1 a may be considered as an element inwhich the resistance value oscillates with a fixed cycle at a frequencycorresponding to the spin torque resonance frequency. With this effect,the element impedance at the frequency equal to the spin torqueresonance frequency of the magnetoresistive effect element 1 a isreduced. The connection of the first port 9 a, the magnetoresistiveeffect element 1 a, and the second port 9 b in series in this orderenables the high-frequency signal to be cut off at a non-resonantfrequency with high impedance and to be passed at a resonant frequencywith low impedance. In other words, the magnetoresistive effect device100 is capable of having frequency characteristics as the high-frequencyfilter.

The choke coil 10 (impedance element) connected to the signal line 7 andthe ground 8 does not pass the high-frequency signal but selectivelycauses the direct current signal to flow to the ground. Accordingly, thedirect current supplied from the direct-current input terminal 11 flowsthrough the closed circuit including the magnetoresistive effect element1 a, the signal line 7, the choke coil 10 (impedance element), theground 8, and the direct-current input terminal 11. The closed circuitallows the direct current to be efficiently applied to themagnetoresistive effect element 1 a. In response to the application ofthe direct current, the spin torque is increased and the amplitude ofthe oscillating resistance value is increased in the magnetoresistiveeffect element 1 a. Since the increase in the amplitude of theoscillating resistance value increases the amount of change in elementimpedance of the magnetoresistive effect element 1 a, themagnetoresistive effect device 100 functions as the high-frequencyfilter having a wide range of the cut-off characteristics and thebandpass characteristics.

In addition, since varying the direct current applied from thedirect-current input terminal 11 enables the spin torque resonancefrequency of the magnetoresistive effect element 1 a to be variablycontrolled, the magnetoresistive effect device 100 functions as avariable frequency filter.

Furthermore, since the magnetic-field applying mechanism 12 varies themagnetic field to be applied to the magnetoresistive effect element 1 ato vary the spin torque resonance frequency of the magnetoresistiveeffect element 1 a, the magnetoresistive effect device 100 functions asthe variable frequency filter.

Furthermore, since the magnetoresistive effect device 100 does notinclude a magnetoresistive effect element connected to the signal line 7and the ground 8 in parallel with the second port 9 b, themagnetoresistive effect device 100 is capable of preventing the inputhigh-frequency signal from flowing into the ground 8 to prevent anincrease in loss of the high-frequency signal. The flow of thehigh-frequency signal into the ground 8 is caused by a reduction inimpedance at the spin torque resonance frequency of the magnetoresistiveeffect element connected to the signal line 7 and the ground 8 inparallel with the second port 9 b. Accordingly, the magnetoresistiveeffect device 100 functions as a high-frequency filter having excellentbandpass characteristics.

Various components may be added to the magnetoresistive effect device100 of the first embodiment described above. For example, in order toprevent the direct current signal from flowing into a high-frequencycircuit connected to the first port 9 a, a capacitor for cutting off thedirect current signal may be connected in series to the signal line 7between the first port 9 a and the direct-current input terminal 11.Alternatively, in order to prevent the direct current signal fromflowing into a high-frequency circuit connected to the second port 9 b,a capacitor for cutting off the direct current signal may be connectedin series to the signal line 7 between the second port 9 b and the chokecoil 10.

Second Embodiment

FIG. 4 is a schematic cross-sectional view of a magnetoresistive effectdevice 101 according to a second embodiment of the present invention.Points different from the magnetoresistive effect device 100 of thefirst embodiment in the magnetoresistive effect device 101 will bemainly described and a description of common points will beappropriately omitted herein. The same reference numerals are used inthe second embodiment to identify the same components in themagnetoresistive effect device 100 of the first embodiment and adescription of the common components will be omitted herein. Themagnetoresistive effect device 101 includes two magnetoresistive effectelements 1 a and 1 b each including the magnetization fixed layer 2, thespacer layer 3, and the magnetization free layer 4, the upper electrode5, the lower electrode 6, the first port 9 a, the second port 9 b, thesignal line 7, the choke coil 10 as an impedance element, thedirect-current input terminal 11, and the magnetic-field applyingmechanism 12. The magnetoresistive effect element 1 a is connected inparallel to the magnetoresistive effect element 1 b between the upperelectrode 5 and the lower electrode 6. The first port 9 a, themagnetoresistive effect element 1 a or the magnetoresistive effectelement 1 b, and the second port 9 b are connected in series in thisorder via the signal line 7. The magnetoresistive effect elements 1 aand 1 b have different spin torque resonance frequencies from each otherin a state in which the same magnetic field and the direct currenthaving the same current density are applied. More specifically, althoughthe magnetoresistive effect elements 1 a and 1 b have the same filmstructure and have rectangular shapes in plan view, the plan view shapeof the magnetoresistive effect element 1 a is different from the planview shape of the magnetoresistive effect element 1 a in the aspectratio. “The same film structure” means that the magnetoresistive effectelements 1 a and 1 b have the same material and the same film thicknessof each layer composing the magnetoresistive effect elements and havethe same lamination order of the layers. “The plan view shape” means theshape of each of the magnetoresistive effect elements when themagnetoresistive effect element is viewed from above a planeperpendicular to the stacking direction of the respective layerscomposing the magnetoresistive effect element. “The aspect ratio” meansthe ratio of the length of long sides to the length of short sides of arectangle circumscribed around the plan view shape of themagnetoresistive effect element with a minimum area.

The choke coil 10 is connected to the ground 8 and to the signal line 7between the magnetoresistive effect elements 1 a and 1 b, which areconnected in parallel to each other, and the second port 9 b. Thedirect-current input terminal 11 is connected to the signal line 7 atthe opposite side to the choke coil 10 with the magnetoresistive effectelements 1 a and 1 b in between the direct-current input terminal 11 andthe choke coil 10. The connection of the direct-current source 13connected to the ground 8 to the direct-current input terminal 11 formsa closed circuit including the magnetoresistive effect element 1 a, themagnetoresistive effect element 1 b, the signal line 7, the choke coil10, the ground 8, and the direct-current input terminal 11. The directcurrent supplied from the direct-current input terminal 11 flows throughthe closed circuit and is applied to the magnetoresistive effect element1 a and the magnetoresistive effect element 1 b.

The magnetization free layer 4 of the magnetoresistive effect element 1a and the magnetization free layer 4 of the magnetoresistive effectelement 1 b are connected to the same upper electrode 5. Themagnetization fixed layer 2 of the magnetoresistive effect element 1 aand the magnetization fixed layer 2 of the magnetoresistive effectelement 1 b are connected to the same lower electrode 6.

The magnetic-field applying mechanism 12 is disposed near themagnetoresistive effect elements 1 a and 1 b and simultaneously appliesthe same magnetic field to the magnetoresistive effect elements 1 a and1 b. The magnetic-field applying mechanism 12 varies the magnetic fieldsto be applied to the magnetoresistive effect elements 1 a and 1 b tovary the spin torque resonance frequencies of the magnetoresistiveeffect elements 1 a and 1 b.

The film structures of the magnetoresistive effect elements 1 a and 1 bare the same as the film structure of the magnetoresistive effectelement 1 a of the first embodiment. FIG. 5 is a top view of themagnetoresistive effect device 101. As illustrated in FIG. 5, themagnetoresistive effect elements 1 a and 1 b have the same dimension Y₀in the Y direction, which is the direction of the short sides of theplan view shapes of the magnetoresistive effect elements 1 a and 1 b.However, a dimension Xa in the X direction, which is the direction ofthe long sides of the plane view shape of the magnetoresistive effectelement 1 a, is different from a dimension Xb in the X direction, whichis the direction of the long sides of the plane view shape of themagnetoresistive effect element 1 b, and Xa<Xb. Accordingly, the aspectratio (Xb/Y₀) of the plan view shape of the magnetoresistive effectelement 1 b is higher than the aspect ratio (Xa/Y₀) of the plan viewshape of the magnetoresistive effect element 1 a. In consideration of astate in which the same magnetic field and the direct current of thesame current density are applied to each magnetoresistive effectelement, the spin torque resonance frequency of the magnetoresistiveeffect element is increased with an increase in aspect ratio of the planview shape of the magnetoresistive effect element. As a result, a spintorque resonance frequency fb of the magnetoresistive effect element 1 bis higher than a spin torque resonance frequency fa of themagnetoresistive effect element 1 a. Since differentiating the aspectratios of the plan view shapes of the multiple magnetoresistive effectelements in the above manner enables the spin torque resonancefrequencies to be differentiated from each other even when themagnetoresistive effect elements have the same film structure, it ispossible to manufacture the multiple magnetoresistive effect elementshaving different spin torque resonance frequencies from each otherthrough the same film formation process. In other words, since themultiple magnetoresistive effect elements have the same film structure,it is possible to collectively form the films of the layers composingthe multiple magnetoresistive effect elements.

Due to the spin torque resonance phenomenon, the frequency componentsthat coincide with the spin torque resonance frequency of themagnetoresistive effect element 1 a or the magnetoresistive effectelement 1 b or that are near the spin torque resonance frequency of themagnetoresistive effect element 1 a or the magnetoresistive effectelement 1 b, among the high-frequency components of the high-frequencysignal input through the first port 9 a, pass through themagnetoresistive effect element 1 a or the magnetoresistive effectelement 1 b in a low impedance state and are supplied to the second port9 b. In other words, the magnetoresistive effect device 101 functions asa high-frequency filter using the frequencies near the spin torqueresonance frequency of the magnetoresistive effect element la or themagnetoresistive effect element 1 b as the passband.

FIG. 6 is a graph illustrating the relationship between the frequency ofthe high-frequency signal input into the magnetoresistive effect device101 and the attenuation. Referring to FIG. 6, the vertical axisrepresents attenuation and the horizontal axis represents frequency. Asillustrated in FIG. 6, differentiating the aspect ratios of the planview shapes of the magnetoresistive effect elements 1 a and 1 b fromeach other so that part of the frequencies near the spin torqueresonance frequency fa of the magnetoresistive effect element 1 a (apassband 200 a illustrated in FIG. 6) is overlapped with part of thefrequencies near the spin torque resonance frequency fb of themagnetoresistive effect element 1 b (a passband 200 b illustrated inFIG. 6) allows the magnetoresistive effect device 101 to have a passband(a passband 200 illustrated in FIG. 6) wider than that of themagnetoresistive effect device 100 of the first embodiment, asillustrated in FIG. 6.

In addition, varying the direct current to be applied to themagnetoresistive effect elements 1 a and 1 b or the strength of themagnetic field to be applied from the magnetic-field applying mechanism12 to the magnetoresistive effect elements 1 a and 1 b enables thebandwidth of the magnetoresistive effect device 101 to be arbitrarilyvaried. Accordingly, the magnetoresistive effect device 101 functions asa variable frequency filter capable of arbitrarily varying the passband.

As described above, since the magnetoresistive effect elements 1 a and 1b having different spin torque resonance frequencies from each other areconnected in parallel to each other in the magnetoresistive effectdevice 101, the impedance of the multiple magnetoresistive effectelements near the multiple frequencies equal to the spin torqueresonance frequencies of the respective magnetoresistive effect elementsis reduced and the passband 200 having a certain width is provided. Inaddition, varying the direct current or the magnetic field to be appliedto the magnetoresistive effect elements enables the positions of thepassbands to be varied. In other words, the magnetoresistive effectdevice 101 functions as a variable frequency filter capable of varyingthe position of the passband.

Furthermore, since the plan view shapes of the multiple magnetoresistiveeffect elements 1 a and 1 b have different aspect ratios from each otherin the magnetoresistive effect device 101, it is possible to manufacturethe multiple magnetoresistive effect elements 1 a and 1 b havingdifferent spin torque resonance frequencies from each other through thesame process. Specifically, since the multiple magnetoresistive effectelements 1 a and 1 b have the same film structure in themagnetoresistive effect device 101, it is possible to collectively formthe films of the layers composing the multiple magnetoresistive effectelements 1 a and 1 b, thereby reducing the manufacturing cost.

Although the two magnetoresistive effect elements 1 a and 1 b havingdifferent spin torque resonance frequencies from each other areconnected in parallel in the magnetoresistive effect device 101 of thesecond embodiment, three or more magnetoresistive effect elements havingdifferent spin torque resonance frequencies from each other may beconnected in parallel. In this case, the width of the passband isfurther increased.

Although the two magnetoresistive effect elements 1 a and 1 b have thesame film structure in the magnetoresistive effect device 101 of thesecond embodiment, the multiple magnetoresistive effect elements mayhave different film structures. In this case, the different filmstructures may be used while the aspect ratios of the plane view shapesof the multiple magnetoresistive effect elements are made equal to eachother to differentiate the spin torque resonance frequencies of themultiple magnetoresistive effect elements from each other.

Although the same magnetic field is simultaneously applied to the twomagnetoresistive effect elements 1 a and 1 b by the magnetic-fieldapplying mechanism 12 in the magnetoresistive effect device 101 of thesecond embodiment, magnetic-field applying mechanisms for individuallyapplying the magnetic fields to the respective magnetoresistive effectelements may be provided.

Third Embodiment

FIG. 7 is a schematic cross-sectional view of a magnetoresistive effectdevice 102 according to a third embodiment of the present invention.Points different from the magnetoresistive effect device 100 of thefirst embodiment in the magnetoresistive effect device 102 will bemainly described and a description of common points will beappropriately omitted herein. The same reference numerals are used inthe third embodiment to identify the same components in themagnetoresistive effect device 100 of the first embodiment and adescription of the common components will be omitted herein. Themagnetoresistive effect device 102 includes two magnetoresistive effectelements 1 a each including the magnetization fixed layer 2, the spacerlayer 3, and the magnetization free layer 4, the upper electrode 5, thelower electrode 6, the first port 9 a, the second port 9 b, the signalline 7, the choke coil 10 as an impedance element, the direct-currentinput terminal 11, and two magnetic-field applying mechanisms 12. Thetwo magnetoresistive effect elements 1 a have the same configuration andare connected in parallel to each other between the upper electrode 5and the lower electrode 6. The first port 9 a, the two magnetoresistiveeffect elements 1 a connected in parallel to each other, and the secondport 9 b are connected in series in this order via the signal line 7.Each of the magnetic-field applying mechanisms 12 applies an individualmagnetic field to the corresponding magnetoresistive effect element 1 a.As described above, the magnetoresistive effect device 102 includes thetwo magnetic-field applying mechanisms 12 capable of applying anindividual magnetic field to each of the two magnetoresistive effectelements 1 a. The choke coil 10 is connected to the ground 8 and to thesignal line 7 between the two magnetoresistive effect elements 1 aconnected in parallel to each other and the second port 9 b. Thedirect-current input terminal 11 is connected to the signal line 7 atthe opposite side to the choke coil 10 with the two magnetoresistiveeffect elements 1 a, which are connected in parallel to each other, inbetween the direct-current input terminal 11 and the choke coil 10. Theconnection of the direct-current source 13 connected to the ground 8 tothe direct-current input terminal 11 forms a closed circuit includingthe magnetoresistive effect elements 1 a, the signal line 7, the chokecoil 10, the ground 8, and the direct-current input terminal 11. Thedirect current supplied from the direct-current input terminal 11 flowsthrough the closed circuit and is applied to the two magnetoresistiveeffect elements 1 a.

The magnetization free layers 4 of the two magnetoresistive effectelements 1 a are connected to the same upper electrode 5. Themagnetization fixed layers 2 of the two magnetoresistive effect elements1 a are connected to the same lower electrode 6.

In the magnetoresistive effect device 102, the high-frequency signal issupplied to the two magnetoresistive effect elements 1 a via the signalline 7 in a state in which the magnetic fields are individually appliedfrom the respective magnetic-field applying mechanisms 12 to thecorresponding magnetoresistive effect elements 1 a. For example, thestrength of the magnetic field to be applied to one of themagnetoresistive effect elements 1 a is made smaller than the strengthof the magnetic field to be applied to the other of the magnetoresistiveeffect elements 1 a. Since the spin torque resonance frequencies of themagnetoresistive effect elements 1 a are increased with an increase instrengths of the applied magnetic fields, the spin torque resonancefrequencies of the two magnetoresistive effect elements 1 a aredifferent from each other in this case.

Due to the spin torque resonance phenomenon, the frequency componentsthat coincide with the spin torque resonance frequency of either of thetwo magnetoresistive effect elements 1 a or that are near the spintorque resonance frequency of either of the two magnetoresistive effectelements 1 a, among the high-frequency components of the high-frequencysignal input through the first port 9 a, pass through themagnetoresistive effect elements 1 a in a low impedance state and aresupplied to the second port 9 b. In other words, the magnetoresistiveeffect device 102 functions as a high-frequency filter using thefrequencies near the spin torque resonance frequency of either of thetwo magnetoresistive effect elements 1 a as the passband.

FIG. 8 is a graph illustrating the relationship between the frequency ofthe high-frequency signal input into the magnetoresistive effect device102 and the attenuation. Referring to FIG. 8, the vertical axisrepresents attenuation and the horizontal axis represents frequency. Forexample, as illustrated in FIG. 8, when the magnetic field to be appliedto one of the magnetoresistive effect elements 1 a is made smaller thanthe magnetic field to be applied to the other of the magnetoresistiveeffect elements 1 a, f1<f2 where f1 denotes the spin torque resonancefrequency of the one of the magnetoresistive effect elements 1 a and f2denotes the spin torque resonance frequency of the other of themagnetoresistive effect elements 1 a. Accordingly, as illustrated inFIG. 8, adjusting the strength of the magnetic field to be applied fromeach of the magnetic-field applying mechanisms 12 to the correspondingmagnetoresistive effect element 1 a so that part of the frequencies nearthe spin torque resonance frequency f1 of the one of themagnetoresistive effect elements 1 a (a passband 300 a illustrated inFIG. 8) is overlapped with part of the frequencies near the spin torqueresonance frequency f2 of the other of the magnetoresistive effectelements 1 a (a passband 300 b illustrated in FIG. 8) allows themagnetoresistive effect device 102 to have a passband (a passband 300illustrated in FIG. 8) wider than that of the magnetoresistive effectdevice 100 of the first embodiment, as illustrated in FIG. 8.

In addition, varying the direct current to be applied to each of themagnetoresistive effect elements 1 a or the strength of the magneticfield to be applied from each of the magnetic-field applying mechanisms12 to the corresponding magnetoresistive effect element 1 a enables thebandwidth of the magnetoresistive effect device 102 to be arbitrarilyvaried. Accordingly, the magnetoresistive effect device 102 functions asa variable frequency filter capable of arbitrarily varying the passband.

As described above, since the magnetoresistive effect device 102 has themultiple magnetic-field applying mechanisms 12 so as to apply anindividual magnetic field to each of the multiple magnetoresistiveeffect elements 1 a, the magnetoresistive effect device 102 is capableof individually controlling the spin torque resonance frequencies of therespective magnetoresistive effect elements 1 a. In addition, since themultiple magnetoresistive effect elements 1 a are connected in parallelto each other, the impedance of the multiple magnetoresistive effectelements near the multiple frequencies equal to the spin torqueresonance frequencies of the respective magnetoresistive effect elements1 a is reduced and the passband 300 having a certain width is provided.Furthermore, varying the direct current or the magnetic field to beapplied to each of the magnetoresistive effect elements 1 a enables thebandwidth of the magnetoresistive effect device 102 to be arbitrarilyvaried. Accordingly, the magnetoresistive effect device 102 functions asthe variable frequency filter capable of arbitrarily varying thepassband.

In addition, although the two magnetoresistive effect elements 1 a areconnected in parallel to each other and the two magnetic-field applyingmechanisms 12 for individually applying the magnetic fields to therespective magnetoresistive effect elements 1 a are provided in themagnetoresistive effect device 102 of the third embodiment, three ormore magnetoresistive effect elements 1 a may be connected in parallelto each other and three of more magnetic-field applying mechanisms 12for individually applying the magnetic fields to the respectivemagnetoresistive effect elements 1 a may be provided. In this case, itis possible to further increase the width of the passband.

Furthermore, although the two magnetoresistive effect elements 1 a havethe same configuration in the magnetoresistive effect device 102 of thethird embodiment, the multiple magnetoresistive effect elements may havedifferent configurations.

Fourth Embodiment

FIG. 9 is a schematic cross-sectional view of a magnetoresistive effectdevice 103 according to a fourth embodiment of the present invention.Points different from the magnetoresistive effect device 100 of thefirst embodiment in the magnetoresistive effect device 103 will bemainly described and a description of common points will beappropriately omitted herein. The same reference numerals are used inthe fourth embodiment to identify the same components in themagnetoresistive effect device 100 of the first embodiment and adescription of the common components will be omitted herein. Themagnetoresistive effect device 103 includes the two magnetoresistiveeffect elements 1 a and 1 b each including the magnetization fixed layer2, the spacer layer 3, and the magnetization free layer 4, upperelectrodes 5 a and 5 b, lower electrodes 6 a and 6 b, the first port 9a, the second port 9 b, the signal line 7, the choke coil 10 as animpedance element, the direct-current input terminal 11, and themagnetic-field applying mechanism 12. The upper electrode 5 a and thelower electrode 6 a are disposed so as to sandwich the magnetoresistiveeffect element 1 a therebetween and the upper electrode 5 b and thelower electrode 6 b are disposed so as to sandwich the magnetoresistiveeffect element 1 b therebetween. The magnetoresistive effect element 1 ais connected in series to the magnetoresistive effect element 1 b. Thefirst port 9 a, the magnetoresistive effect element 1 a, themagnetoresistive effect element 1 b, and the second port 9 b areconnected in series in this order via the signal line 7. Themagnetoresistive effect elements 1 a and 1 b have different spin torqueresonance frequencies from each other in a state in which the samemagnetic field and the direct current having the same current densityare applied. More specifically, although the magnetoresistive effectelements 1 a and 1 b have the same film structure and have rectangularshapes in plan view, the plan view shape of the magnetoresistive effectelement 1 a is different from the plan view shape of themagnetoresistive effect element 1 a in the aspect ratio. “The same filmstructure” means that the magnetoresistive effect elements 1 a and 1 bhave the same material and the same film thickness of each layercomposing the magnetoresistive effect elements and have the samelamination order of the layers. “The plan view shape” means the shape ofeach of the magnetoresistive effect elements when the magnetoresistiveeffect element is viewed from above a plane perpendicular to thestacking direction of the respective layers composing themagnetoresistive effect element. “The aspect ratio” means the ratio ofthe length of long sides to the length of short sides of a rectanglecircumscribed around the plan view shape of the magnetoresistive effectelement with a minimum area.

The choke coil 10 is connected to the ground 8 and to the signal line 7between the magnetoresistive effect element 1 b and the second port 9 b.The direct-current input terminal 11 is connected to the signal line 7at the opposite side to the choke coil 10 with the magnetoresistiveeffect element 1 a and the magnetoresistive effect element 1 b inbetween the direct-current input terminal 11 and the choke coil 10. Theconnection of the direct-current source 13 connected to the ground 8 tothe direct-current input terminal 11 forms a closed circuit includingthe magnetoresistive effect element 1 a, the magnetoresistive effectelement 1 b, the signal line 7, the choke coil 10, the ground 8, and thedirect-current input terminal 11. The direct current supplied from thedirect-current input terminal 11 flows through the closed circuit and isapplied to the magnetoresistive effect element 1 a and themagnetoresistive effect element 1 b.

The lower electrode 6 a to which the magnetization fixed layer 2 of themagnetoresistive effect element 1 a is connected is electricallyconnected to the upper electrode 5 b to which the magnetization freelayer 4 of the magnetoresistive effect element 1 b is connected. Themagnetoresistive effect elements 1 a and 1 b are connected in series toeach other.

The magnetic-field applying mechanism 12 is disposed near themagnetoresistive effect elements 1 a and 1 b and simultaneously appliesthe same magnetic field to the magnetoresistive effect elements 1 a and1 b. The magnetic-field applying mechanism 12 varies the magnetic fieldsto be applied to the magnetoresistive effect elements 1 a and 1 b tovary the spin torque resonance frequencies of the magnetoresistiveeffect elements 1 a and 1 b.

The film structures of the magnetoresistive effect elements 1 a and 1 bare the same as the film structure of the magnetoresistive effectelement 1 a of the first embodiment. FIG. 10 is a top view of themagnetoresistive effect device 103. As illustrated in FIG. 10, themagnetoresistive effect elements 1 a and 1 b have the same dimension Y₀in the Y direction, which is the direction of the short sides of theplan view shapes of the magnetoresistive effect elements 1 a and 1 b.However, the dimension Xa in the X direction, which is the direction ofthe long sides of the plane view shape of the magnetoresistive effectelement 1 a, is different from the dimension Xb in the X direction,which is the direction of the long sides of the plane view shape of themagnetoresistive effect element 1 b, and Xa<Xb. Accordingly, the aspectratio (Xb/Y₀) of the plan view shape of the magnetoresistive effectelement 1 b is higher than the aspect ratio (Xa/Y₀) of the plan viewshape of the magnetoresistive effect element 1 a. In consideration ofthe state in which the same magnetic field and the direct current of thesame current density are applied to each magnetoresistive effectelement, the spin torque resonance frequency of the magnetoresistiveeffect element is increased with an increase in aspect ratio of the planview shape of the magnetoresistive effect element. As a result, the spintorque resonance frequency fb of the magnetoresistive effect element 1 bis higher than the spin torque resonance frequency fa of themagnetoresistive effect element 1 a. Since differentiating the aspectratios of the plan view shapes of the multiple magnetoresistive effectelements in the above manner enables the spin torque resonancefrequencies to be differentiated from each other even when themagnetoresistive effect elements have the same film structure, it ispossible to manufacture the multiple magnetoresistive effect elementshaving different spin torque resonance frequencies from each otherthrough the same film formation process. In other words, since themultiple magnetoresistive effect elements have the same film structure,it is possible to collectively form the films of the layers composingthe multiple magnetoresistive effect elements. In addition, in themagnetoresistive effect device 103, since the magnetoresistive effectelements 1 a and 1 b are connected in series to each other and the areaof the cross section of the magnetoresistive effect element 1 a in adirection perpendicular to the direction in which the direct currentflows is smaller than the area of the cross section of themagnetoresistive effect element 1 b in the direction, the currentdensity of the direct current applied to the magnetoresistive effectelement 1 a is higher than that of the direct current applied to themagnetoresistive effect element 1 b. As described above, the spin torqueresonance frequency of the magnetoresistive effect element is reducedwith an increase in current density of the applied direct current.Accordingly, the plan view shape of the magnetoresistive effect element1 a is different from the plan view shape of the magnetoresistive effectelement 1 b in the aspect ratio and the current density of the applieddirect current and fa<fb.

Due to the spin torque resonance phenomenon, the frequency componentsthat coincide with the spin torque resonance frequency of themagnetoresistive effect element 1 a or the magnetoresistive effectelement 1 b or that are near the spin torque resonance frequency of themagnetoresistive effect element 1 a or the magnetoresistive effectelement 1 b, among the high-frequency components of the high-frequencysignal input through the first port 9 a, pass through themagnetoresistive effect element 1 a and the magnetoresistive effectelement 1 b in a low impedance state, which are connected in series toeach other, and are supplied to the second port 9 b. In other words, themagnetoresistive effect device 103 functions as a high-frequency filterusing the frequencies near the spin torque resonance frequency of themagnetoresistive effect element 1 a or the magnetoresistive effectelement 1 b as the passband.

FIG. 11 is a graph illustrating the relationship between the frequencyof the high-frequency signal input into the magnetoresistive effectdevice 103 and the attenuation. Referring to FIG. 11, the vertical axisrepresents attenuation and the horizontal axis represents frequency. Asillustrated in FIG. 11, differentiating the aspect ratios of the planview shapes of the magnetoresistive effect elements 1 a and 1 b fromeach other so that part of the frequencies near the spin torqueresonance frequency fa of the magnetoresistive effect element 1 a (apassband 400 a illustrated in FIG. 11) is overlapped with part of thefrequencies near the spin torque resonance frequency fb of themagnetoresistive effect element 1 b (a passband 400 b illustrated inFIG. 11) allows the magnetoresistive effect device 103 to have apassband (a passband 400 illustrated in FIG. 11) wider than that of themagnetoresistive effect device 100 of the first embodiment, asillustrated in FIG. 11.

In addition, varying the direct current to be applied to themagnetoresistive effect elements 1 a and 1 b or the strength of themagnetic field to be applied from the magnetic-field applying mechanism12 to the magnetoresistive effect elements 1 a and 1 b enables thebandwidth of the magnetoresistive effect device 103 to be arbitrarilyvaried. Accordingly, the magnetoresistive effect device 103 functions asa variable frequency filter capable of arbitrarily varying the passband.

As described above, since the multiple magnetoresistive effect elements1 a and 1 b having different spin torque resonance frequencies from eachother are connected in series to each other in the magnetoresistiveeffect device 103, the impedance of the multiple magnetoresistive effectelements near the multiple frequencies equal to the spin torqueresonance frequencies of the respective magnetoresistive effect elementsis reduced and the passband 400 having a certain width is provided. Inaddition, varying the direct current or the magnetic field to be appliedto the magnetoresistive effect elements enables the positions of thepassbands to be varied. In other words, the magnetoresistive effectdevice 103 functions as a variable frequency filter capable of varyingthe position of the passband.

Furthermore, since the plan view shapes of the multiple magnetoresistiveeffect elements 1 a and 1 b have different aspect ratios from each otherin the magnetoresistive effect device 103, it is possible to manufacturethe multiple magnetoresistive effect elements 1 a and 1 b havingdifferent spin torque resonance frequencies from each other through thesame process. Specifically, since the multiple magnetoresistive effectelements 1 a and 1 b have the same film structure in themagnetoresistive effect device 103, it is possible to collectively formthe films of the layers composing the multiple magnetoresistive effectelements 1 a and 1 b, thereby reducing the manufacturing cost.

Although the two magnetoresistive effect elements 1 a and 1 b havingdifferent spin torque resonance frequencies from each other areconnected in series to each other in the magnetoresistive effect device103 of the fourth embodiment, three or more magnetoresistive effectelements having different spin torque resonance frequencies from eachother may be connected in series to each other. In this case, the widthof the passband is further increased.

Although the two magnetoresistive effect elements 1 a and 1 b have thesame film structure in the magnetoresistive effect device 103 of thefourth embodiment, the multiple magnetoresistive effect elements mayhave different film structures. In this case, the different filmstructures may be used while the aspect ratios of the plane view shapesof the multiple magnetoresistive effect elements are made equal to eachother to differentiate the spin torque resonance frequencies of themultiple magnetoresistive effect elements from each other.

Although the same magnetic field is simultaneously applied to themagnetoresistive effect elements 1 a and 1 b by the magnetic-fieldapplying mechanism 12 in the magnetoresistive effect device 103 of thefourth embodiment, magnetic-field applying mechanisms for individuallyapplying the magnetic fields to the respective magnetoresistive effectelements may be provided, as in the third embodiment.

Fifth Embodiment

FIG. 12 is a schematic cross-sectional view of a magnetoresistive effectdevice 104 according to a fifth embodiment of the present invention.Points different from the magnetoresistive effect device 100 of thefirst embodiment in the magnetoresistive effect device 104 will bemainly described and a description of common points will beappropriately omitted herein. The same reference numerals are used inthe fifth embodiment to identify the same components in themagnetoresistive effect device 100 of the first embodiment and adescription of the common components will be omitted herein. Themagnetoresistive effect device 104 includes the two magnetoresistiveeffect elements 1 a each including the magnetization fixed layer 2, thespacer layer 3, and the magnetization free layer 4, the upper electrodes5 a and 5 b, the lower electrodes 6 a and 6 b, the first port 9 a, thesecond port 9 b, the signal line 7, the choke coil 10 as an impedanceelement, the direct-current input terminal 11, and the twomagnetic-field applying mechanisms 12. The two magnetoresistive effectelements 1 a have the same configuration. The upper electrode 5 a andthe lower electrode 6 a are disposed so as to sandwich themagnetoresistive effect element 1 a therebetween and the upper electrode5 b and the lower electrode 6 b are disposed so as to sandwich themagnetoresistive effect element 1 b therebetween. The twomagnetoresistive effect elements 1 a are connected in series to eachother. The first port 9 a, the magnetoresistive effect elements 1 a, andthe second port 9 b are connected in series in this order via the signalline 7. Each of the magnetic-field applying mechanisms 12 applies anindividual magnetic field to the corresponding magnetoresistive effectelement 1 a. As described above, the magnetoresistive effect device 104includes the two magnetic-field applying mechanisms 12 capable ofapplying an individual magnetic field to each of the twomagnetoresistive effect elements 1 a. The choke coil 10 is connected tothe ground 8 and to the signal line 7 between the two magnetoresistiveeffect elements 1 a connected in series to each other and the secondport 9 b. The direct-current input terminal 11 is connected to thesignal line 7 at the opposite side to the choke coil 10 with the twomagnetoresistive effect elements 1 a, which are connected in series toeach other, between the direct-current input terminal 11 and the chokecoil 10. The connection of the direct-current source 13 connected to theground 8 to the direct-current input terminal 11 forms a closed circuitincluding the two magnetoresistive effect elements 1 a connected inseries to each other, the signal line 7, the choke coil 10, the ground8, and the direct-current input terminal 11. The direct current suppliedfrom the direct-current input terminal 11 flows through the closedcircuit and is applied to the two magnetoresistive effect elements 1 a.

The lower electrode 6 a to which the magnetization fixed layer 2 of oneof the magnetoresistive effect elements 1 a is connected is electricallyconnected to the upper electrode 5 b to which the magnetization freelayer 4 of the other of the magnetoresistive effect elements 1 a isconnected. The two magnetoresistive effect elements 1 a are connected inseries to each other.

In the magnetoresistive effect device 104, the high-frequency signal issupplied to the two magnetoresistive effect elements 1 a via the signalline 7 in a state in which the magnetic fields are individually appliedfrom the respective magnetic-field applying mechanisms 12 to thecorresponding magnetoresistive effect elements 1 a. For example, thestrength of the magnetic field to be applied to one of themagnetoresistive effect elements 1 a is made smaller than the strengthof the magnetic field to be applied to the other of the magnetoresistiveeffect elements 1 a. Since the spin torque resonance frequencies of themagnetoresistive effect elements 1 a are increased with an increase instrengths of the applied magnetic fields, the spin torque resonancefrequencies of the two magnetoresistive effect elements 1 a aredifferent from each other in this case.

Due to the spin torque resonance phenomenon, the frequency componentsthat coincide with the spin torque resonance frequency of either of thetwo magnetoresistive effect elements 1 a or that are near the spintorque resonance frequency of either of the two magnetoresistive effectelements 1 a, among the high-frequency components of the high-frequencysignal input through the first port 9 a, pass through the twomagnetoresistive effect elements 1 a in a low impedance state, which areconnected in series to each other, and are supplied to the second port 9b. In other words, the magnetoresistive effect device 104 functions as ahigh-frequency filter using the frequencies near the spin torqueresonance frequency of either of the two magnetoresistive effectelements 1 a as the passband.

FIG. 13 is a graph illustrating the relationship between the frequencyof the high-frequency signal input into the magnetoresistive effectdevice 104 and the attenuation. Referring to FIG. 13, the vertical axisrepresents attenuation and the horizontal axis represents frequency. Forexample, as illustrated in FIG. 13, when the magnetic field to beapplied to one of the magnetoresistive effect elements 1 a is madesmaller than the magnetic field to be applied to the other of themagnetoresistive effect elements 1 a, f1<f2 where f1 denotes the spintorque resonance frequency of the one of the magnetoresistive effectelements 1 a and f2 denotes the spin torque resonance frequency of theother of the magnetoresistive effect elements 1 a. Accordingly, asillustrated in FIG. 13, adjusting the strength of the magnetic field tobe applied from each of the magnetic-field applying mechanisms 12 to thecorresponding magnetoresistive effect element 1 a so that part of thefrequencies near the spin torque resonance frequency f1 of the one ofthe magnetoresistive effect elements 1 a (a passband 500 a illustratedin FIG. 13) is overlapped with part of the frequencies near the spintorque resonance frequency f2 of the other of the magnetoresistiveeffect elements 1 a (a passband 500 b illustrated in FIG. 13) allows themagnetoresistive effect device 104 to have a passband (a passband 500illustrated in FIG. 13) wider than that of the magnetoresistive effectdevice 100 of the first embodiment, as illustrated in FIG. 13.

In addition, varying the direct current to be applied to each of themagnetoresistive effect elements 1 a or the strength of the magneticfield to be applied from each of the magnetic-field applying mechanisms12 to the corresponding magnetoresistive effect element 1 a enables thebandwidth of the magnetoresistive effect device 104 to be arbitrarilyvaried. Accordingly, the magnetoresistive effect device 104 functions asa variable frequency filter capable of arbitrarily varying the passband.

As described above, since the magnetoresistive effect device 104 has themultiple magnetic-field applying mechanisms 12 so as to apply anindividual magnetic field to each of the multiple magnetoresistiveeffect elements 1 a, the magnetoresistive effect device 104 is capableof individually controlling the spin torque resonance frequencies of therespective magnetoresistive effect elements 1 a. In addition, since themultiple magnetoresistive effect elements 1 a are connected in series toeach other, the impedance of the multiple magnetoresistive effectelements near the multiple frequencies equal to the spin torqueresonance frequencies of the respective magnetoresistive effect elements1 a is reduced and the passband 500 having a certain width is provided.Furthermore, varying the direct current or the magnetic field to beapplied to each of the magnetoresistive effect elements 1 a enables thebandwidth of the magnetoresistive effect device 104 to be arbitrarilyvaried. Accordingly, the magnetoresistive effect device 104 functions asthe variable frequency filter capable of arbitrarily varying thepassband.

In addition, although the two magnetoresistive effect elements 1 a areconnected in series to each other and the two magnetic-field applyingmechanisms 12 for individually applying the magnetic fields to therespective magnetoresistive effect elements 1 a are provided in themagnetoresistive effect device 104 of the fifth embodiment, three ormore magnetoresistive effect elements 1 a may be connected in series toeach other and three of more magnetic-field applying mechanisms 12 forindividually applying the magnetic fields to the respectivemagnetoresistive effect elements 1 a may be provided. In this case, itis possible to further increase the width of the passband.

Furthermore, although the two magnetoresistive effect elements 1 a havethe same configuration in the magnetoresistive effect device 104 of thefifth embodiment, the multiple magnetoresistive effect elements may havedifferent configurations.

Although the embodiments of the present invention have been describedabove, it will be clear that the present invention is not limited tothese specific examples and embodiments and that many changes andmodified embodiments will be obvious to those skilled in the art. Forexample, although the examples are described in the first to fifthembodiment in which the choke coil 10 is connected to the ground 8 andto the signal line 7 between the magnetoresistive effect element 1 a (1b) and the second port 9 b and the direct-current input terminal 11 isconnected to the signal line 7 between the magnetoresistive effectelement 1 a (1 b) and the first port 9 a, the choke coil 10 may beconnected to the ground 8 and to the signal line 7 between themagnetoresistive effect element 1 a (1 b) and the first port 9 a and thedirect-current input terminal 11 may be connected to the signal line 7between the magnetoresistive effect element 1 a (1 b) and the secondport 9 b.

Although the example in which the choke coil 10 is used as the impedanceelement is described above in the first to fifth embodiments, aresistance element may be used as the impedance element, instead of thechoke coil 10. In this case, the resistance element is connected betweenthe signal line 7 and the ground 8 and has a function to cut off thehigh-frequency components of the current with its resistance component.The resistance element may be a chip resistor or a resistor composed ofa pattern line. The resistance element preferably has a resistance valueof the characteristic impedance of the signal line 7 or more. Forexample, when the signal line 7 has a characteristic impedance of 50 Ω,45% of the high-frequency power is capable of being cut off with theresistance element when the resistance element has a resistance value of50Ω and 90% of the high-frequency power is capable of being cut off withthe resistance element when the resistance element has a resistancevalue of 500Ω. The use of the resistance element enables direct currentapplied from the direct-current input terminal 11 to flow through theclosed circuit including the magnetoresistive effect element 1 a (1 b),the signal line 7, the resistance element, the ground 8, and thedirect-current input terminal 11 without degrading the characteristicsof the high-frequency signal passing through the magnetoresistive effectelement 1 a (1 b).

When the resistance element is used as the impedance element, it ispreferred that a capacitor for cutting off the direct current signal isconnected in series to the signal line 7 between the first port 9 a andthe direct-current input terminal 11 (or the resistance element) and acapacitor for cutting off the direct current signal is connected inseries to the signal line 7 between the second port 9 b and theresistance element (or the direct-current input terminal 11). Thisbecause it is possible to cause the direct current applied from thedirect-current input terminal 11 to efficiently flow through the closedcircuit including the magnetoresistive effect element 1 a (1 b), thesignal line 7, the resistance element, the ground 8, and thedirect-current input terminal 11.

What is claimed is:
 1. A magnetoresistive effect device comprising: at least one magnetoresistive effect element; a first port through which a high-frequency signal is input; a second port through which a high-frequency signal is output; a signal line; an impedance element; and a direct-current input terminal, wherein the first port, the magnetoresistive effect element, and the second port are connected in series in this order via the signal line, wherein the impedance element (i) is connected to the signal line between the magnetoresistive effect element and the first port or the second port, and (ii) is further able to be connected to a ground; wherein the direct-current input terminal is connected to the signal line, and the magnetoresistive effect element is between (i) a location at which the impedance element is connected to the signal line, and (ii) a location at which the direct-current input terminal is connected to the signal line, and wherein the magnetoresistive effect device is able to form a closed circuit when it is connected to the ground, where the closed circuit includes the magnetoresistive effect element, the signal line, the impedance element, the ground, and the direct-current input terminal.
 2. The magnetoresistive effect device according to claim 1, further comprising at least one magnetic-field applying mechanism that is configured to apply a magnetic field to the magnetoresistive effect element.
 3. The magnetoresistive effect device according to claim 2, wherein the magnetic-field applying mechanism is configured to vary the magnetic field to vary a spin torque resonance frequency of the magnetoresistive effect element.
 4. The magnetoresistive effect device according to claim 1, wherein the at least one magnetoresistive effect element includes a plurality of magnetoresistive effect elements having different spin torque resonance frequencies from each other, and wherein the magnetoresistive effect elements are connected in parallel to each other.
 5. The magnetoresistive effect device according to claim 2, wherein the at least one magnetoresistive effect element includes a plurality of magnetoresistive effect elements, wherein the at least one magnetic-field applying mechanism includes a plurality of magnetic-field applying mechanisms, and wherein the magnetoresistive effect elements are connected in parallel to each other and the magnetic-field applying mechanisms are provided so as to apply an individual magnetic field to each of the magnetoresistive effect elements.
 6. The magnetoresistive effect device according to claim 1, wherein the at least one magnetoresistive effect element includes a plurality of magnetoresistive effect elements having different spin torque resonance frequencies from each other, and wherein the magnetoresistive effect elements are connected in series to each other.
 7. The magnetoresistive effect device according to claim 2, wherein the at least one magnetoresistive effect element includes a plurality of magnetoresistive effect elements, wherein the at least one magnetic-field applying mechanism includes a plurality of magnetic-field applying mechanisms, and wherein the magnetoresistive effect elements are connected in series to each other and the magnetic-field applying mechanisms are provided so as to apply an individual magnetic field to each of the magnetoresistive effect elements.
 8. The magnetoresistive effect device according to claim 4, wherein plan view shapes of the magnetoresistive effect elements having different spin torque resonance frequencies from each other have different aspect ratios from each other.
 9. The magnetoresistive effect device according to claim 6, wherein plan view shapes of the magnetoresistive effect elements having different spin torque resonance frequencies from each other have different aspect ratios from each other.
 10. The magnetoresistive effect device according to claim 1, wherein the magnetoresistive effect device does not include a magnetoresistive effect element connected to the signal line and the ground in parallel with the second port. 